Sunday, October 4, 2009

Arctic seas turn to acid, putting vital food chain at risk

With the world's oceans absorbing six million tonnes of carbon a day, a leading oceanographer warns of eco disaster

Carbon-dioxide emissions are turning the waters of the Arctic Ocean into acid at an unprecedented rate, scientists have discovered. Research carried out in the archipelago of Svalbard has shown in many regions around the north pole seawater is likely to reach corrosive levels within 10 years. The water will then start to dissolve the shells of mussels and other shellfish and cause major disruption to the food chain. By the end of the century, the entire Arctic Ocean will be corrosively acidic.

"This is extremely worrying," Professor Jean-Pierre Gattuso, of France's Centre National de la Recherche Scientifique, told an international oceanography conference last week. "We knew that the seas were getting more acidic and this would disrupt the ability of shellfish – like mussels – to grow their shells. But now we realise the situation is much worse. The water will become so acidic it will actually dissolve the shells of living shellfish."

Just as an acid descaler breaks apart limescale inside a kettle, so the shells that protect molluscs and other creatures will be dissolved. "This will affect the whole food chain, including the North Atlantic salmon, which feeds on molluscs," said Gattuso, speaking at a European commission conference, Oceans of Tomorrow, in Barcelona last week. The oceanographer told delegates that the problem of ocean acidification was worse in high latitudes, in the Arctic and around Antarctica, than it was nearer the equator.

"More carbon dioxide can dissolve in cold water than warm," he said. "Hence the problem of acidification is worse in the Arctic than in the tropics, though we have only recently got round to studying the problem in detail."

About a quarter of the carbon dioxide pumped into the atmosphere by factories, power stations and cars now ends up being absorbed by the oceans. That represents more than six million tonnes of carbon a day.

This carbon dioxide dissolves and is turned into carbonic acid, causing the oceans to become more acidic. "We knew the Arctic would be particularly badly affected when we started our studies but I did not anticipate the extent of the problem," said Gattuso.

His research suggests that 10% of the Arctic Ocean will be corrosively acidic by 2018; 50% by 2050; and 100% ocean by 2100. "Over the whole planet, there will be a threefold increase in the average acidity of the oceans, which is unprecedented during the past 20 million years. That level of acidification will cause immense damage to the ecosystem and the food chain, particularly in the Arctic," he added.

The tiny mollusc Limacina helicina, which is found in Arctic waters, will be particularly vulnerable, he said. The little shellfish is eaten by baleen whales, salmon, herring and various seabirds. Its disappearance would therefore have a major impact on the entire marine food chain. The deep-water coral Lophelia pertusa would also be extremely vulnerable to rising acidity. Reefs in high latitudes are constructed by only one or two types of coral – unlike tropical coral reefs which are built by a large variety of species. The loss of Lophelia pertusa would therefore devastate reefs off Norway and the coast of Scotland, removing underwater shelters that are exploited by dozens of species of fish and other creatures.

"Scientists have proposed all sorts of geo-engineering solutions to global warming," said Gattuso. "For instance, they have proposed spraying the upper atmosphere with aerosol particles that would reduce sunlight reaching the Earth, mitigating the warming caused by rising levels of carbon dioxide.

"But these ideas miss the point. They will still allow carbon dioxide emissions to continue to increase – and thus the oceans to become more and more acidic. There is only one way to stop the devastation the oceans are now facing and that is to limit carbon-dioxide emissions as a matter of urgency."

This was backed by other speakers at the conference. Daniel Conley, of Lund University, Sweden, said that increasing acidity levels, sea-level rises and temperature changes now threatened to bring about irreversible loss of biodiversity in the sea. Christoph Heinze, of Bergen University, Norway, said his studies, part of the EU CarboOcean project, had found that carbon from the atmosphere was being transported into the oceans' deeper waters far more rapidly than expected and was already having a corrosive effect on life forms there.

The oceans' vulnerability to climate change and rising carbon-dioxide levels has also been a key factor in the launching of the EU's Tara Ocean project at Barcelona. The expedition, on the sailing ship Tara, will take three years to circumnavigate the globe, culminating in a voyage through the icy Northwest Passage in Canada, and will make continual and detailed samplings of seawater to study its life forms.

A litre of seawater contains between 1bn and 10bn single-celled organisms called prokaryotes, between 10bn and 100bn viruses and a vast number of more complex, microscopic creatures known as zooplankton, said Chris Bowler, a marine biologist on Tara.

"People think they are just swimming in water when they go for a dip in the sea," he said. "In fact, they are bathing in a plankton soup."

That plankton soup is of crucial importance to the planet, he added. "As much carbon dioxide is absorbed by plankton as is absorbed by tropical rainforests. Its health is therefore of crucial importance to us all."

However, only 1% of the life forms found in the sea have been properly identified and studied, said Bowler. "The aim of the Tara project is to correct some of that ignorance and identify many more of these organisms while we still have the chance. Issues like ocean acidification, rising sea levels and global warming will not be concerns at the back of our minds. They will be a key focus for the work that we do while we are on our expedition."

The toll by 2100

■ The Intergovernmental Panel on Climate Change forecast in 2007 that sea levels would rise by 20cm to 60cm by 2100 thanks to global warming caused by man-made carbon-dioxide emissions. This is now thought to be an underestimate, however, with most scientific bodies warning that sea levels could rise by a metre or even higher. Major inundations of vulnerable regions such as Bangladesh would ensue.

■ The planet will be hotter by 3C by 2100, most scientists now expect, though rises of 4.5C to 5C could be experienced. Deserts will spread and heatwaves will become more prevalent. Ice-caps will melt and cyclones are also likely to be triggered.

■ Weather patterns across the globe will become more unstable, numbers of devastating storms will increase dramatically while snow will disappear from all but the highest mountains.